


Energy Swapping, Demon Style!

by DCJoKeRHS



Category: Gravity Falls
Genre: (Not), (maybe), Aphrodisiacs, Barely Legal, Bill Cipher Has A Sheath, Bottom Dipper Pines, Come Inflation, Could Be Canon, Demon Bill Cipher, Dipper is 17, Dirty Talk, Established Relationship, Fucked Up, Hahaha There Already, How Do I Tag, I Don't Even Know, I'm Going to Hell, M/M, Older Dipper Pines, Possessive Bill Cipher, Shameless Smut, Teenage Dipper Pines, Tentacle Dick, Top Bill Cipher, Triangle Bill Cipher, Why Did I Write This?
Language: English
Status: Completed
Published: 2018-01-11
Updated: 2018-08-06
Packaged: 2019-03-03 14:49:08
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 3,220
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13343475
Author URL: https://archiveofourown.org/users/DCJoKeRHS/pseuds/DCJoKeRHS
Summary: I dreamed of this, it's been haunting me for weeks and FUCK YES it deserves it's own fic as a whacko-oneshot!OK, so, Dipper and Bill have been dating //foreeeeever//, and Bill's gotten a bit possessive, so wants to take things the next step, which Dipper's really just a confuzzled darling over, until there's the word "mating" coming from Bill's vocabulary...Things go crazy from there ;D





	1. Chapter 1

**Author's Note:**

  * For [Chromatic_Demon123](https://archiveofourown.org/users/Chromatic_Demon123/gifts).



“Pinetree…”

Dipper looks up from his book, before smiling.

“Bill!” he beams.

“Hey, Pinetree,” Bill smiles, cupping Dipper’s cheek, “You know I love you?”

“Uh-huh?” Dipper’s joyful expression turns curious.

“Can I make it official?”

Dipper pauses.

“Official? You mean like marriage?”

This obtains a chuckle from Bill.

“It’s something a lot stronger than that; I am a Demon, after all; pitiful, holy bits of paper like that won’t work like that.”

Dipper tilts his head, as Bill moves so his eye is centimetres from Dipper’s face.

“I take some of your energy in exchange for mine, using something akin to that mating ritual that results in children for you humans…”

“You mean sex?!” Dipper asks, surprised.

Bill pauses, finding the link, before nodding.

“However, by swapping energies, we’re placed closer to eachother’s sort of… Level; you will gain demonic traits, though not really change that much physically, unless you so desire, meanwhile I-…”

“You’d be more of a Human…” Dipper breathes, raising a hand to rest on Bill’s side, which Bill takes in his other hand.

“We do it enough times, then we’ll both be halflings; won’t that be beautiful?” Bill smiles, eye becoming a mouth for a moment as he kisses the palm of Dipper’s hand.

Dipper looks surprised, before a slow blush brims over his cheeks.

“I mean, I do get horny thinking of you… But who would top? Plus, what if I’m not horny enough…?”

Bill chuckles, before kissing Dipper’s forehead.

“I’ll give you an aphrodisiac, alright?” Bill says gently.

“Then… I’m free for the rest of the afternoon, and everyone’s out…” Dipper hums.

He smiles, kissing Bill’s upper eyelid/lip.

Bill smirks, as Dipper finds Bill’s lips/eyelids returning the kiss, gently being guided to his own bed, where he’s gently lain down, legs spread, Bill pulling out a vial, which he dips his finger into, the finger then stretching, before resting over Dipper’s lips.

Dipper gently takes the finger into his mouth, licking it clean like a lolly, Bill turning a slightly pinkish hue, as he then repeats the process twice more, the vial then disappearing.

“So… How does this work?” Diper asks.

“I’ll show you, you just need to relax, my dearest Sapling,” Bill purrs, as he gently starts removing Dipper’s clothes, the feeling of the warm liquid Bill had given him slipping into his blood, as Dipper goes limp and relaxed, before starting to feel warm all over.

Fingers drift over his chest, stroking over hardening nipples, which has a gasp leaning Dipper’s lips, Bill’s eye turning lustful as he starts to fondle them, Dipper whimpering as he then feels Bill moving one hand to his slowly-building arousal, as a cool tongue licks his stomach.

Dipper jerks up into the movement, whining, as the lips go lower, before, finally, wrapping around his length, Dipper looking down to see Bill starting to suck him off.

“Holy-…” Dipper breathes.

He thought Bill wouldn’t enjoy this kind of stuff, yet with how he's acting _now_ …

Bill releases him when Dipper feels half-there, as Dipper’s eyes are locked on him.

Floating up slightly, the hand that had been at Dipper’s chest glides down to continue gently tugging lightly at Dipper’s cock, as Dipper’s eyes widen, open mouth watering as a black tendril droops, before slowly sliding from inbetween Bill’s legs, the thin thing floating until it has weaved around.

“No going back now, Pinetree,” Bill rasps, eye primal, as Dipper sees the tendril lower…

He didn’t expect the wet feeling at his rear entrance, as it gently starts pumping its way in, Dipper whining when it strokes something like a match, before rubbing gently against it, as Bill lowers, the tenta-dick reaching further, until Dipper can feeling it resting against his spine, at the small of his back, his legs over the sides of Bill’s triangular body as half his ass presses into the polished-wood-like-surface of Bill, buried to the root.

Then Bill _moves_ , the rubbing like a string over his innards, before it starts to thicken with soft pulses, as Dipper looks round at the feeling of two things dropping to slap the rest of his ass and part of his back, which is raised off the bed.

Two melon-sized balls of the same, black “skin” stare back.

Dipper feels close, pressing down and rubbing against Bill, before a hand wraps around his cock, harshly.

“We come together,” Bill growls, as Dipper whines.

“Please, Bill… Your Balls are fucking _huge_ , your dick is so _deep_ , _**please**_!” he whines, as the tenta-dick grows thicker, balls slapping Dipper with each long, luxurious thrust, as Dipper starts to feel his hole getting stretched, ass-cheeks pushed apart as Bill manages to sink _Deeper_ , ending up behind Dipper’s floating rib as he stretches Dipper as wide as possible. The only sounds heard are the creaking of the bed, Dipper’s whines, and the melon-balls slapping and bruising Dipper’s butt.

“ _Bill_ ,” Dipper whines, before he feels Bill’s dick _pop_ , crying out as it fills _every crevice_ of his ass and lower abdomen, visible through his stomach.

“ _Dipper_ …”

Bill runts inside him for a few more moments, before realising Dipper’s dick, which has the almost-young adult seeing stars, back arching in a silent scream of ecstasy as he is _filled_ , stomach bulging above him as the tidal wave of Bill’s “cum” fills him, mouth snatching shut as Dipper tries to stop himself from hacking it up onto the duvet, eyes rolling up with a whimper as Bill ruts him through it all, eye not once losing that needful, lustful look as he watches how Dipper wriggles, gone himself to his own high, before he gives a soft breath as he flops onto Dipper, still locked inside, as Dipper swallows the “cum” trying to leave his lips.

“Bill…” Dipper breathes, sinful lips open as he tries to breath, “W-What now?”

“Now,” Bill purrs, “We wait until my dick deflates, which will be once you’ve absorbed all of my beautiful energy. This will take a short while, though the stuff I gave you as an aphrodisiac will help…”

“But what about Mabel? And Stan? And Ford?” Dipper asks softly.

Bill chuckles.

“It won’t take _that_ long… Maybe even enough time for a second round, if you want.”

Dipper lets out a long, wistful, wanting whine.

“About half an hour… See, its already started.”

Dipper looks down to see, indeed, his stomach had deflated slightly, though then he sees his chest.

Carefully, he touches it.

“Huh, looks like your magic does want your body to change…”

His chest had risen, gaining more of a curve, even if he was still quite flat, yet was still very much more bouncy as Dipper poked it.

Bill’s eye watches the finger, before smirking.

Dipper’s eyes widen as his wrist is gently grabbed, and the poking finger stuck into Bill’s mouth…

Yep, he’s definitely up to more.

“Please… I want more of you inside me,” Dipper says softly.

Bill chuckles, rolling him over onto his hands and knees, making Dipper groan at the feeling of the tenta-cock rubbing his insides, as Bill starts rutting him through the absorption process.

Indeed, when Bill’s tenta-dick softens, Bill returns to those long thrusts, though it works Dipper open even more, as Dipper feels the tentadick enter his guts, soon having its tip resting beside his heart.

Bill speeds up, as the elongated dick starts to _buzzzzzzzzz_ , vibrating as Dipper feels his body come alive with hungry fire, jerking back in time with each thrust as Bill’s balls increase volume, growing heavier and reaching down half Dipper’s thighs as Dipper feels like an octupus’ arm is writhing within him, he himself writhing in want as he feels his cock and own testicles tap the rugby-ball sacks of “cum” Bill has the pride of calling _his_.

“Holy _fuck_ , Pinetree, you insatiable _pet_ of _mine_ ,” Bill grunts as Dipper moans, a hand having moved to stroke where he can feel the monster-cock beneath his skin.

“Yes, _yours_ , every _bit_ , as you own _me_ with your thick _cock_ ,” Dipper breathes.

Bill chuckles.

“Indeed, I have _ruined_ you for human mating, made you _mine_ , my pretty _cock-sleeve_ , my perfect _toy_ , take my _cum_ and look _pregnant_ with what’s _mine_ , only cry _my_ name with that hungry, _slutty_ voice of yours,” he growls out, before Dipper cries out.

“ _ **Bill**_!”

His stomach immediately stretches to touch the bed as Bill’s cock is forced out, despite the knot, as Dipper feels his heart tingling, spreading into his blood as his mind is filled with afterglow, pain taking a backseat as he fills the head of Bill’s tenta-dick stopping any cum from leaving, as Dipper feels it working deep into the very _essence_ of himself.

“ _Fuck_ , _**Dipper**_!” Bill growls, as his eye becomes a mouth that bites Dipper’s right, upper arm, blood spilling into his mouth as Dipper moans loud enough to echo, eyes lidded, before he collapses.

When Bill finally pulls away, Dipper looks completely ruined, as the hole in his arm leaves behind a glittery, gold scar from Bill’s teeth, forming the shape of a closed eye.

“That was _perfect_ ,” Bill purrs, cleaning up the mess as he smirks at the way no cum but Dipper’s had spilt on the sheets, his own body absorbing that and tucking it into his depleted energy reserves, as the lack of power pulls him back, though Bill has just enough time to tuck a naked Dipper in, belly still visible, yet no longer bursting with his cum.

“ _You_ are perfect, my dear _Dipper_ …”

 


	2. More Than A Tentadick

The next time Dipper gets to see Bill, by tracing the scar on his arm, Dipper has escaped into the forest.

More specifically, the abandoned laboratory, which Dipper had turned into a functional den.

Which was _exactly_ why he decided to call Bill there.

He'd figured out how to disable the trap on the entrance, taking it out bit-by-bit to replace with a comfy reception, as - after ensuring the entrance into the room holding the incubated shapeshifter was sealed - removed the consoles and found he'd regained quite a surprising amount of space through doing so, being able to fit a second bed, a bookshelf and a desk.

When Bill appears, Dipper notices how his arms and legs were thicker, more human-shaped.

"Dipper!" Bill greets.

Dipper hums, reaching out.

"I missed you," he pouts.

Bill chuckles, arms stretching as they lift Dipper up, Dipper not minding the feeling of himself sinking slightly into pitch-black flesh.

"I remodelled," Dipper hums, pecking a soft kiss to one of Bill's tiles.

"I know! Though I see you don't like that last-remaining shifter you've got next door!"

Dipper looks up.

"Is it so easy to tell?" he asks, curious.

Bill's eye crinkles.

"How you've sealed the door with concrete filing the small de-contamination room through the pipe the decontamination fluid came says it all... Plus the fact they're frozen into your shape."

Dipper lets out a small whine, cuddling closer.

Bill clicks his fingers, letting his magic flow around them, as Dipper finds the room expanding, the bed, too, as he hears the sound of something being squashed.

"Dealt with it!" Bill grins, as he sets Dipper on the bed, "So, aphrodisiac, or are you happy enough to see me without it?"

Dipper blushes.

"A blend of both..." he says.

Bill's eyelids/lips kiss Dipper's forehead.

"How about we start with you riding my face, then!"

Dipper splutters.

"W-what?!" he squeaks, "B-but you lubed me with your- with _that_ last time a-and... I mean, it's not a _no_ , but..."

Dipper's eyes go to the tentacle half-hanging from its sheath.

"I want to... Suck it..." Dipper mutters.

Bill chuckles.

"69-ing it s, then!" Bill grins, why don't you show me what you have then, Dipper?"

Dipper squirms in his lover's lap, before taking a breath.

He moves himself round so he's sitting with his legs on either side of Bill's, starting to gently lick the tiles, eyes turning half-lidded as he gently runs his fingers over Bill's edges.

"Y-you can take my clothes off, Bill," Dipper says, as Bill lets out a soft, sultry chuckle.

A click, and Dipper's clothes are neatly folded nearby, as Dipper shivers at the sudden feeling of air on his behind.

Kissing his way down, Dipper blinks as he gently starts running a hand along Bill's tentacle, working it free gently, as he continues to pump his hand across it, opening his mouth when he sees the tip.

Bill pauses Dipper there, as his eye crinkles, the vial from before appearing.

Dipper lets himself be lifted by his middle, so his face is now over Bill's waist, as he sees a finger coated in the stuff from before placed on the tip of Bill's length, before it gently moves to hover in front of Dipper's mouth.

Dipper hesitantly wraps his mouth around it, as he reaches up to hold it, a moan coming from below, as Dipper licks off the fluid, letting the tentacle feel around...

...Before it darts past Dipper's gag reflex and into the depths of his throat, Dipper yelping around it, as he then carefully lets it work deeper, following it down so he can feel it glide into his belly, lips resting on dark balls that Dipper notices are about the size of his head.

He moans softly, as he reaches up a hand to run around the lumps, as he then feels a thing poke at his rear.

"A~?" Dipper gasps, though his jaw is stretched as wide as possible to accomodate for the thickness of the tentadick inside, as Bill chuckles beneath him.

Then, Dipper realises.

It's Bill's _tongue_.

With a similar texture and quality...

A moan breaks out of Dipper's mouth, as he feels Bill's tongue force it's way inside, only noticing what's happening when he's pulled _up_ , the tongue going deeper as Bill's dick is pulled out.

Combined with the burning now spreading through him again, he can only stay to hold himself up, a whine running through as Bill starts slow, eyes darting down to the open maw beneath his butt, that he's then sat in.

Though, the feeling of a hand winding its way to his own length has a moan leaving him.

Bill starts speeding up, though gentle with his mouth, the feeling of lips on his behind has him jerking his hips with each strike, little breathy grunts leaving his lips as he swallows the length inside him, eyes fluttering and squeezing shut with every thrust, gasps turning to gasped moans as he feels Bill knot his tongue and dick, the lump burning every internal nerve as he moves a hand, _feeling_ his stomach's shape jerking and shifting as Bill moans, speeding up.

The sudden feeling of the knot unravelling, of something bursting deep into his innards, has Dipper and Bill _moaning_ in unison, as Bill's tongue retracts, Dipper shakily forcing his knees under him as he sees and feels the way his belly once again stretches around the sheer amount of cum inside, hooded eyes meeting with Bill's, as Dipper feels up to find the knot in his throat, his own length having spayed all over Bill's bottom eyelid, as Bill's tongue licks it away in one, clan go.

"Our magic is ensuring you can breathe," Bill admits, "You look _really_ hot, right now."

Dipper tries to smile, but only manages to get another, smaller wave of cum spilling into himself.

"So, enjoy that?"

Dipper nods, humming.

He holds up two fingers.

"You want a second round again?"

Dipper nods, as Bill smiles.

"Sure, then."

Dipper mulls over what Bill had said about magic, looking at his fingers.

"You used basic magic with the zombies, channelling the magic you draw to you through your birthmark," Bill states.

Dipper listen as Bill enters scientific detail about how magic works, as his belly slowly dies down.

Purring, Dipper adjusts his position slightly, letting the blood flow return to his legs.

"Bill...?" he asks.

Bill chuckles, as Dipper feels the tentacle slide down his front, eyes widening as it winds down to his rear, as he's suddenly rotated and pulled back with just the power of the dick that shot into him.

"Wha-aa~ah..." Dipper's exclamation turns into a moan as he feels how it brushes inside, arms going weak as Bill _smirks_.

"B-Bill~..." Dipper whines, as Bill carefully lifts him, before dropping him down again, Dipper yelping and whining at the semi-rough treatment, little mewls breaking between each thrust as Bill pounds into him, chuckling darkly.

"Tell me how much you like it," Bill purrs.

"I-I-" Dipper gasps, "Y-you... In me... It's _so- good_! Ah- I, it's so _deep_ a-and th-the fact I kn- _know_ you're going to f-fill me with your cum-... You're, p-pounding into me w-with my heartbeat and i-it's so _full_ b-back a-at my entrance, that you've made yours, that you're _owning_ with e-each _thrust_..." Dipper's watery eyes peer up with a blend of lust, trust and love, Bill chuckling.

"You look _beautiful_ , I can see _every angle_ you're lain in, every _part_ of you as I take such a sweet behind as yours. _Yes_ , you are mine, morphing under _my_ magic, just as I morph under _yours_ , our bodies intertwined with the love and lust that spans _eons_... What would old _Sixer_ sy, were he to see us? But, no, even then I'd probably _destroy_ him for seeing you in a state only _I_ wish to ever be able to see."

Dipper lets out a long, keening whine.

"Y-yes, m-more, I-I like your voice, your dick... _You_ , p-please, _please_!" he begs, as Bill chuckles, rolling them so Dipper lies beneath him, as he starts to thrust _harder_ , Dipper's eyes blowing wide with pleasure as Bill doesn't once stop, tearing into Dipper's behind as he can _feel_ the way Dipper trembles beneath him, _so close_ to the brink, as his sweat and pre-cum are sucked up by Bill's magic, into Bill's bricks, as his cum maps out _every vein_ , every _capillary_ in Dipper's lithe frame, that still retain a slight chub from the way it had swelled up _so much_ from Bill's cum.

Dipper's yelps and mewls turn to cries and screams, ramblings falling from his lips that are thick and plump from the abuse of Bill's cock, as Bill _chuckles_.

"You look so _perfect_ ,  **my** _**Pet**_ ," Bill purrs.

It's enough to shove Dipper over the edge, as he comes with a wail, muscles spasming around the intruder deep inside them.

Dipper's whine turns into moans, asBill feels himself also reach the edge.

"I- 'S fine, come inside me, M-M-M-M _aster_!" Dipper moans, Bill chuckling.

"Of course, my Pineslut," Bill purrs, as his knot pops, the seccond load of cum sloshing into Dipper, as Dipper'shooded eyes land on Bill's eye.

A soft, pleased smile comes to Dipper's face.

"Cuddles?" he asks, reaching up.

Bill blinks, before his eye narrows, the demon curling around his human, as Dipper kisses the a tile just by Bill's eye...

 

The next morning finds Dipper finding he isn't limping by the time he's left the abandoned lab, a grin coming to his face, as he looks at the small belly he still has, squishing the fat with a little chuckle.

_It appears Bill's cum is a good substitute for a full meal..._

**Author's Note:**

> *chuckles*  
> I have a feeling if any of my rl friends see this I'm going to find myself sitting in either the AE room of the hospital or a Psychiatrist's waiting room... ¬w¬  
> ....  
> #NOREGERTS!! \\(>▼<)/


End file.
